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On beyond AncestryDNA

Reader Ida French is having trouble figuring out how third-party utilities like Gedmatch.com can help in using autosomal test results, and particularly those from AncestryDNA. She writes:

I am still having a hard time understanding how exactly this will help. I have uploaded my raw data from Ancestry to Gedmatch and played around with the tools but don’t understand how this can direct me any better to a match than what Ancestry has given us with our DNA matches. One of my matches is on Chromosome 4, 8.5cm and 1,592 snp. We also match on other chromosomes. My question is where do I go from here?

The bottom line here is that what Gedmatch provides, and Ancestry doesn’t, is the ability to see exactly where in your DNA you and another person match.

Let me give you an example. I can look at my own DNA and that of a cousin of mine who has also tested. At Gedmatch, we show this match-up on chromosomes 11 and 12 (among others):

I happen to know exactly in our family lines this cousin and I match, and that he and I have no lines in common other than one set of third great grandparents.

That much, you may say, you can get from AncestryDNA and its shaky-leaf hint system.

But by knowing exactly where in our DNA this cousin and I match, where I can go from here is to look for others who match me and my cousin in the same place in our DNA.

This process of adding others into your match-list mix allows you to share genealogical information with more people who are likely descended from the same common ancestors.

Once you and any DNA cousin have identified a segment as having come from one set of common ancestors, then you know that anyone else in the future who matches you in that same place is also likely to be a cousin in that line.

The problem with Ancestry, of course, is that the tree of the person you match there may be just plain flat out wrong. There is no other information given there except the tree to see if it’s likely to be true or not.

Let me give you an example. One of my own shaky-leaf hints on AncestryDNA is with a woman whose tree says she is a descendant of my Baker family through a fourth great granduncle Henry Baker and then through Henry’s daughter Nancy who, her tree says, married one Jesse Smith and lived and died in Tennessee.

One hitch here. Henry Baker’s daughter Nancy married Robert Wakefield in North Carolina, and she and Robert remained there, married to each other and recorded in census and court records, until they died and were buried there in NC. No Smith and no Tennessee even remotely in Nancy’s history.

If that match and I had both uploaded our information to Gedmatch, or if we had both tested with a company that provides analytical tools, we could see where in our DNA we match — rather than where in faulty online trees. And if either of us had mapped that segment to a particular line, we’d be able to avoid the time wasted in chasing that non-Baker rabbit down into a genealogical black hole.

Alternatively, had I mapped that shared segment to my Baker ancestors, we’d know to spend more time seeing where in the Baker family that match really belongs, since her descent isn’t in any supposed Smith-Baker marriage.

The downside of Gedmatch, or any third party utility, of course, is that not all those who test uploads their DNA data to the utility site. That means you can only compare your results to those who have uploaded there. But at least when you do compare it, you’re comparing apples to apples and oranges to oranges, rather than one possibly faulty tree to another possibly faulty tree.

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